The present invention relates to chairs of which the seat is raisable, and more particularly to chairs of this type designed for theaters.
In a theater, of course, the minimum distance between chairs of two successive rows is governed by safety standards. This distance is reckoned between the most projecting part of a chair of a given row with respect to the backrest of the chair of the preceding row. It is therefore essential, in order to be able to install the maximum number of chairs in a theater of given size, for the seat to be raisable as much as possible against the backrest.
The minimum overall dimension is determined by the length of the armrests designed in view of comfort if the raised seat is entirely received between these armrests. Chairs comprising two lateral legs to which are fixed two hinge casings generally have this minimum overall dimension determined by that of the armrests. However, the mounting of seat assemblies of this type is complex and the number of parts to be adjusted important. Moreover, the lateral position of the legs can constitute a constraint for the spectators and the appearance thereof is unattractive.
These drawbacks have been avoided by chairs with raisable seats for which the support means comprise a single central leg, such as that described in French Pat. No. 2 155 042.
In this case, a single hinge casing is fixed to the leg, and the seat is connected to the casing through its rear edge.
However, the overall dimension of these chairs is relatively large, since the rear of the seat cushion abuts against the backrest in its raised position so that the front edge of the seat projects distinctly forward of the end portion of the armrest. Here the overall dimension which must be satisfied to respect the safety standards is hence determined, not by the armrests, but by the raised seat.
In addition, considering the distance between the hinge axis and the center of gravity of the seat, a very powerful return spring is necessary to obtain automatic raising, and the hinge casing supporting considerable forces, it is of very heavy construction. The large return force necessary generally involves the use of a helical spring mounted around the hinge axis and working in torsion. This type of use causes fairly rapid fatigue of the spring, which, associated with the contingent wear of the cushions, results in a raised position less and less high with time as well as variations in the raised position over a row. These variations constitute a threat to safety, detract from the appearance and entail upkeep costs.
Finally, in known chairs with a raisable seat, the hinge casings are welded to the support means or fixed to the latter at a well-determined angle with respect to its axis. The assembly of the support means and the casing must therefore be adapted to the slope of the floor on which the chair must be fixed, in order that the slope of the seat may correspond to the conformation of the theater. If on delivery, there appears a difference between the theoretical and the actual slopes, the whole stock of support means and casings of all the chairs must be changed or chocks must be used, enormously complicating installation. On the other hand, the angle formed with the floor by the axis of the support means varies with the theater, and if a support cover is required, it must be manufactured to order.